Mycoplasma virus L2 is an enveloped DNA virus, which has a noncytocidal productive infection cycle (with maturation by budding through the cell membrane) followed by the establishment of lysogeny in each infected cell (with the viral genome integrated into the cell chromosome). The unique properties of this virus and experimental advantages of mycoplasmas are the basis of this proposal to investigate several fundamental problems in molecular virology. The proposal has three goals. First, viral genetics will be developed in the genetic code limited mycoplasmas; this will involve DNA sequencing, transcription-translation systems, temperature-sensitive mutants, and other mycoplasma virus variants. Second, the regulatory mechanisms involved in lysogeny and integration vs. noncytocidal productive infection will be determined; this will involve transcriptional control, location of replication origin and terminus, functional analysis of temperature-sensitive mutants, and analysis of the lysogenic state. Third, events in assembly and maturation of the enveloped budding L2 virus will be investigated; this will involve assembly intermediates and membrane assembly. Therefore, this proposal will utilize the experimental advantages of a prokaryotic system to ask questions in molecular virology that generally relate to animal viruses.